#include <iostream>
#include <fstream>
#include <vector>
#include <stack>

using namespace std;

ifstream in("ctc.in");
ofstream out("ctc.out");

int n, m, ctc;
stack<int> s;
vector<vector<int>> graph, trans, ans;
bool fr[100100];

void DFS(int node)
{
    fr[node] = true;

    for(int i : graph[node])
        if(fr[i] == false)
            DFS(i);

    s.push(node);
}

void transDFS(int node)
{
    fr[node] = false;
    ans[ctc].push_back(node);

    cout << ctc << ' ' << node << '\n';

    for(int i : trans[node])
        if(fr[i] == true)
            transDFS(i);
}

void kosaraju()
{
    for(int i = 1; i <= n; i++)
        if(fr[i] == false)
            DFS(i);

    //cout << "got here";
    ans.resize(n + 5);

    while(!s.empty())
    {
        //cout << s.top();

        if(fr[s.top()] == true)
        {
            ctc++;
            transDFS(s.top());
        }

        s.pop();
    }
}

int main()
{
    in >> n >> m;

    graph.resize(n + 5);
    trans.resize(n + 5);

    for(int i = 1; i <= m; i++)
    {
        int x, y;
        in >> x >> y;

        graph[x].push_back(y);
        trans[y].push_back(x);
    }

    kosaraju();

    out << ctc << '\n';

    for(int i = 1; i <= ctc; i++)
    {
        for(int j : ans[i])
            out << j << ' ';

        out << '\n';
    }

    return 0;
}